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Mixed Chloride/Phosphine Complexes of the Dirhenium Core. 3. Novel Structures with Diethylphosphido-bridges and Terminal Diethylphosphines

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posted on 24.10.1998, 00:00 by F. Albert Cotton, Evgeny V. Dikarev, Marina A. Petrukhina
The interaction between octachlorodirhenium anions and diethylphosphine has been shown to strongly depend on reaction conditions, mainly the nature of the solvent and the amount of phosphine. As a result, novel dirhenium products with oxidation states ranging from ReII to ReIV have been obtained. The reaction of [Re2Cl8]2- with an excess of PEt2H in dichloromethane or acetonitrile led to the first example of a face-sharing complex of rhenium(IV) with three phosphido-bridges, namely [Bun4N][Re2(μ-PEt2)3Cl6] (1). The unusual edge-sharing Re2(μ-PEt2)2Cl4(PEt2H)4 (2) complex of rhenium(III) with Ci core symmetry, containing both terminal phosphines and phosphido-bridges, has been obtained by carrying out the reaction with an excess of PEt2H in a benzene (or propanol) − HCl mixture at room temperature. A new example of the 1,2,7,8-type of dirhenium(II) complex, Re2Cl4(PEt2H)4 (3), having diethylphosphine ligands located cis on each Re atom, has been isolated from the reaction of [Re2Cl8]2- with PEt2H in an ethanol-HCl medium. The solid-state structures of complexes 13 have been investigated by X-ray crystallography. Complexes 1 and 2 both crystallized in two forms:  [Bun4N][Re2(μ-PEt2)3Cl6] 1a, P21/n with a = 10.482(1) Å, b = 16.512(2) Å, c = 23.986(2) Å, β = 93.637(8)°, and Z = 4; [Bun4N][Re2(μ-PEt2)3Cl6]·1.5 C7H8 1b, C2/c with a = 38.746(9) Å, b = 10.322(2) Å, c = 27.277(3) Å, β = 110.35(1)°, and Z = 8; Re2(μ-PEt2)2Cl4(PEt2H)4 2a, P21/n with a = 11.081(3) Å, b = 11.029(3) Å, c = 15.627(2) Å, β = 90.05(1)°, and Z = 2; 2b, P21/c with a = 16.094(3) Å, b = 15.193(3) Å, c = 15.548(3) Å, β = 100.98(3)°, and Z = 4. X-ray data for complex Re2Cl4(PEt2H)4 3 are as follows: P21/n with a = 10.445(2) Å, b = 10.113(3) Å, c = 13.473(2) Å, β = 102.17(2)°, and Z = 2. Three bridging μ-PEt2 groups in the face-sharing complex 1 span a short metal−metal distance of 2.4060(6) Å, averaged over 1a and 1b, with a small Re−PEt2−Re angle of 61.34(7)°. The rhenium−rhenium bond length in the edge−sharing complex 2 is 2.7545(7) Å, averaged over 2a and 2b, while the bridging Re−PEt2−Re angle is 72.16(6)°, and the P−Re−P angle for the terminal phosphine ligands is 87.11(7)°. The Re−Re bond distance in 3, 2.2533(8) Å, is typical for triply bonded dirhenium complexes, and the P−Re−P angle for the cis phosphine groups is 93.12(6)°.

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